Widespread use is now being made of piezoelectric audio transducers which comprise generally of a thin sheet metal substrate having ceramic piezoelectric material on one surface thereof. Such transducers are frequently manufactured in the form of a flat relatively thin disc, common sizes having a diameter of about 27 millimeters and 35 millimeters. Transducers of this type are being used in telephone equipment, in smoke alarms, in electronic games, in warning devices on automobiles, and under many similar circumstances where a relatively small tone-generating device is required.
It is common practice to support, or mount, a disc-like audio transducer in a separate plastic housing which can be mounted on a circuit board containing the driving circuit or mounted adjacent to the circuit board. At least two, and sometimes three, wires must be connected to one surface of the transducer and this is commonly done by simply soldering the ends of the wires to the appropriate locations on the transducer. These soldered connections are not entirely satisfactory from a performance standpoint and they are objectionable from a manufacturing standpoint. Since the wires must be soldered to predetermined locations on the transducer, the soldering operation must be carried out by hand, a time-consuming and expensive procedure. Furthermore, the heat of the soldering iron may damage the transducer and the surface to which the wires are soldered must be rendered receptive to the solder and this may require some special treatment, such as tin plating the surface and providing a suitable solder flux thereon.
It has been recognized in the past that it would be desirable to use stamped and formed contact terminals for establishing contact with piezoelectric transducers, since terminals can be produced at relatively low cost, can be connected to wires which extend to the driving circuit by automatic crimping machines, and are generally preferable to hand soldering as a means of establishing electrical contact. However, the service requirements of contact terminals used for transducers present several problems which are not encountered under ordinary circumstances in which contact terminals are used. For example, when a transducer is energized or driven, it vibrates at a frequency of 3,000 cps or more, and a spring contact which is in engagement with the transducer will therefore be flexed at the same frequency. Repeating flexure of a spring contact at this frequency may cause fatigue failures in most commonly used spring contacts, for example, spring contacts of the types used in switches, for the reason that such contacts are designed for use under static conditions with only occasional flexing. Furthermore, contacts which would be used for a piezoelectric device would necessarily be relatively small (as noted above, a commonly used transducer has a diameter of only 27 mm) and the spring arms or spring members of such a contact would necessarily be relatively short. The short, relatively stiff spring would be highly susceptible to fatigue failure when flexed at a frequency of 3,000 cps. A further consideration is that the terminals for an inexpensive transducer assembly would, of necessity, be produced with a minimum amount of relatively inexpensive spring material, such as a spring hard brass, rather than a relatively high priced material which would be resistant to fatigue failure.
The present invention is directed to the achievement of a transducer housing assembly containing contact terminals arranged in the housing such that the transducer disc is contacted by the terminals when the transducer is assembled to the housing. The invention is further directed to the achievement of an assembly which will contain terminals that are resistant to fatigue failure and which will last for the useful life of the device in which the transducer is used.
The transducer housing assembly, in accordance with the invention, comprises generally a molded insulating housing having a recess therein in which there are provided supporting surfaces for supporting the transducer in spaced relationship to the inner end of the recess. Two, or sometimes three, contact terminals are mounting in terminal-receiving wells which extend into the inner end surface of the recess beneath the transducer. Each terminal has a body portion which is retained in the well and a cantilever spring extending at an acute angle from the body portion of the terminal. The spring of each terminal extends obliquely towards the transducer and has a contact portion which is resiliently biased against, and in engagement with, the surface of the transducer. The arrangement is such that the housing diameter is only slightly greater than the diameter of the transducer and the thickness of the housing is well within reasonable limits with regard to the size of the transducer and the circumstances (use in hand-held games or the like) under which it is used. By virtue of the fact that the contact springs extend at a relatively small acute angle from the body portions of the terminals, the fatigue resistance of the individual spring is very good and the contacts are capable of use without failure during the expected life of the transducer.